1. Field of the Invention
The present invention relates to an apparatus for cutting a substrate, and more particularly, to an apparatus for cutting a liquid crystal display panel fabricated on a large-sized mother substrate into individual liquid crystal display panel units.
2. Discussion of the Related Art
In general, a liquid crystal display device is a display device where data signals corresponding to picture information are individually supplied to liquid crystal cells arranged in a matrix form in the display device. Light transmittance of the liquid crystal cells is controlled based on the data signals to display a desired picture.
The liquid crystal display apparatus generally is fabricated by forming thin film transistor array substrates on a large-sized mother substrate, forming color filter substrates on a separate mother substrate and bonding the two mother substrates to each other, thereby simultaneously fabricating multiple individual liquid crystal display panel units and thereby improving fabrication yield. Such a fabrication requires a process for cutting the large-sized mother substrates to form individual liquid crystal display panel units.
The cutting process for the liquid crystal display panels is generally carried out by forming a groove on the surface of the mother substrate using a wheel and applying a force on the mother substrate to form a crack (split) along the groove, thereby cutting the mother substrate into multiple liquid crystal display panel units.
FIG. 1 is a view of a cutting wheel for a liquid crystal display panel of the related art. In FIG. 1, a cutting wheel 10 includes a circular body 11, a cutting blade 12 protruded along an edge of the circular body 11, a hole 13 provided at a central portion of the circular body 11, and a support spindle 14 placed through the hole 13. The cutting blade 12 of the cutting wheel 10 is closely attached on a substrate 15 with certain pressure and rotates in a state of being supported by the support spindle 14 to form a groove having a certain depth on a surface of the substrate 15. After the groove is formed on the substrate 15, a force is applied downwardly on the surface of the substrate 15 to form a crack (split) along the groove, thereby cutting the substrate 15.
FIG. 2 is a view of the cutting wheel of FIG. 1 coupled to a holder 16. In FIG. 2, the holder 16 includes a first opening at a bottom surface and a second opening at a vertical surface, such that the cutting wheel 10 is placed in the holder 16 from the first opening and the support spindle 14 is placed in the holder 16 and through the hole 13 of the cutting wheel 10 from the second opening. The holder 16 also includes a cover 17 for closing the second opening.
FIGS. 3 and 4 are cross-sectional views of the cutting wheel of FIG. 1. In FIG. 3, the cutting wheel 10 has a width of about 0.64 mm and upper and lower isolation intervals between the cutting wheel 10 and the support spindle 14 are respectively set to be about 5 μm. When the cutting wheel 10 is used to form a groove of a certain depth on a surface of a substrate, the cutting wheel 10 can be shaken laterally due to a tolerance (generally, 10-25 μm) in inserting the support spindle 14 into the cutting wheel 10. For example, if the cutting wheel 10 is shaken, an actual isolation interval between the cutting wheel 10 and the support spindle 14 becomes about 10 μm, and the cutting wheel 10 is shaken at an angle θ1 of 0.89°, thereby distorting the rotation of the cutting wheel 10.
In FIG. 4, as the cutting wheel 10 is shaken, friction occurs at the hole 13 between the circular body 11 and the support spindle 14, thereby grinding the central portion of the cutting wheel 10 around the hole 13. In particular, since the cutting wheel 10 is shaken at an angle, the abrasion of this central portion becomes more severe toward its outer edges. Subsequently, an angle θ1 of FIG. 3 becomes larger as the cutting wheel 10 is being used.
In addition, when the cutting wheel 10 is used to form a groove on a surface of the substrate 15, the cutting blade 12 is also abraded due to friction between the cutting blade 12 and the substrate 15 caused by the shaking of the cutting wheel 10. Subsequently, the cutting blade 12 may not maintain being perpendicular to the substrate 15, and a groove is formed irregularly on the surface of the substrate 15.
Further, because the support spindle 14 typically has a material harder than the substrate 15, a degree of abrasion due to friction between the cutting wheel 10 and the support spindle 14 is greater than a degree of abrasion due to friction between the cutting blade 12 and the substrate 15. Accordingly the degree of abrasion due to the friction between the cutting wheel 10 and the support spindle 14 determines a life span of the cutting wheel 10. Thus, the cutting wheel 10 has to be changed even though the cutting blade 12 is not severely abraded and is still usable. Accordingly, an operation of such a cutting equipment is frequently stopped, thereby reducing productivity and increasing cost.